May 9 – Danish-Prussian War (Second War of Schleswig) – Battle of Heligoland: the navy of Denmark and the allied navies of Austria and Prussia fought near the island of Heligoland with a tactical victory for Denmark. It was the last significant naval battle fought by squadrons of wooden ships and also the last one involving Denmark.

December 4 – American Civil War – Sherman's March to the Sea: At Waynesboro, Georgia, forces under Union General Judson Kilpatrick prevent troops led by Confederate General Joseph Wheeler from interfering with Union General Sherman's campaign of destroying a wide swath of the South on his march to Savannah, GA (Union forces suffer more than 3 times the casualties as the Confederates, however).